menreeq wrote:I may have replied to this in the past, but I'll do a brief response. I am a radiologist, but this is NOT medical advice. I saw some information in the other posts that I wanted to comment on.
CT has better spatial resolution than MRI, but MRI has better contrast resolution. They have different pros/cons. CT slices can be as thin as 0.625 mm. MR slices tend to be significantly bigger (5 mm for example) -- depending on the protocol that is in use, which varies from place to place. But "spots" will show up as bright on the MRI on certain sequences, so they can be easier to see. Regarding "regular" CT vs "multiphase" CT --> it really depends what is meant by "regular." If it is without contrast, mets are very difficult to see. CT for CRC mets should be done with contrast, but sometimes people cannot have contrast for other reasons. Multiphase CT means you do multiple CT exams in different phases of where the contrast is in your body (no contrast, contrast in the arteries, contrast in the portal veins, contrast in the systemic veins, delayed phases, etc) -- and this also depends on the protocol being used by your hospital or imaging center. Seeing the liver in different phases makes it easier to see "spots." Ultrasound is less sensitive than CT and MRI, so this is not typically recommended in the US, but may be recommended in other healthcare settings. Ultrasound is less expensive and has no radiation. PET/CT requires that a lesion be at least 8mm to be detected (sometimes smaller spots can be detected if they are very active).
If a "spot" is less than 8-10mm, it can be difficult to tell on CT if it contains water only (a cyst). The phrase "too small to characterize" is often used. If it's bigger than 10mm, looks like water (this is determine by density on CT and signal on MRI), and does not enhance (meaning the contrast gets into it and it gets brighter), it is called a cyst (a benign finding). Anything that does not meet the criteria for water or that enhances is looked at much more carefully --> maybe it is a complex cyst, a benign liver tumor, or cancer. There are many enhancing tumors in the liver that are not cancer, and they have certain patterns on CT and MRI (especially the latter) that a radiologist can evaluate. But if your CT is for colon cancer surveillance, the radiologist is looking with special attention to where CRC mets go (liver, lungs, brain, peritoneum, ovaries, bones, etc). Fatty infiltration looks different than a "spot" - it is shaped differently and not as well defined. It looks different from typical metastases. Small mets will be indistinguishable from benign lesions, which is why surveillance and looking at change over time is necessary, as well as following CEA levels and any other markers that are helpful for that cancer.
I hope everyone's spots stay small and benign!
Static500 wrote:My CT recent scan during final CAPOX cycle in Feb showed NED with the v small liver spots unchanged (this radiologist - rather than classifying them as cysts or fatty deposition - stated that differential diagnosis of these spots included cysts and hemangiomas). However, my most recent CEA has climbed again to 4.6 to continue the trend over the three months of chemo. This has prompted the oncologist to act as although it often rises during chemo the concern is that time to recurrence and risk of recurrence is higher with the BRAF V600E mutation and CT scans can often be clear for a number of months after CEA starts to rise before a met shows on the scan (if that is what is causing the CEA to increase). Thus my next CT scan has been brought forward from Sep to Jun and colonoscopy brought forward too. Another option we discussed was doing a PET scan now incase it shows something not picked up by the CT but in the end decided to go with the earlier CT and colonoscopy route. I’m pretty relaxed about it as think chemo is the most likely reason for the rise and in absolute terms the level isn’t that high albeit it is trending up consistently.
I_will_fight wrote:Static500 wrote:My CT recent scan during final CAPOX cycle in Feb showed NED with the v small liver spots unchanged (this radiologist - rather than classifying them as cysts or fatty deposition - stated that differential diagnosis of these spots included cysts and hemangiomas). However, my most recent CEA has climbed again to 4.6 to continue the trend over the three months of chemo. This has prompted the oncologist to act as although it often rises during chemo the concern is that time to recurrence and risk of recurrence is higher with the BRAF V600E mutation and CT scans can often be clear for a number of months after CEA starts to rise before a met shows on the scan (if that is what is causing the CEA to increase). Thus my next CT scan has been brought forward from Sep to Jun and colonoscopy brought forward too. Another option we discussed was doing a PET scan now incase it shows something not picked up by the CT but in the end decided to go with the earlier CT and colonoscopy route. I’m pretty relaxed about it as think chemo is the most likely reason for the rise and in absolute terms the level isn’t that high albeit it is trending up consistently.
Yeap, I think if they are small PET might not pick them up (it seems PET is not reliable for lesions under 8mm)
I understand MRI might be best to diagnose liver lesions and has the advantage of not being relatively harmless (no radiation). Have you considered it?
Good luck
jts wrote:I have a similar problem ATM. A MRI in December showed a 5mm thing in my liver that the radiologist judged to be a cyst. Looking at my most recent CT scans, the thing is clearly visible (once you know it's there), but in the CT it's just a slightly darker spot in one slice. In the MRI you can make out a high-intensity center surrounded by a dark shell, whereas the rest of the liver looks greyish with whitish vasculature.
Anyhow, the cyst is visible in my CT scans back to late last summer, but not visible before that. So it's safe to say the blob is either new or growing. Meanwhile the upward trend of my CEA continues with a new high measurement in January.
The MRI also notes a smaller cyst in my kidney, but my amateur eyes have trouble seeing it. That is a much less likely location for mets, anyhow.
There are some open access papers talking about how to distinguish between benign and metastatic liver cysts on MRI.
"Differentiating metastatic mucinous colorectal adenocarcinomas from simple cysts of the liver using contrast-enhanced and diffusion-weighted MRI" is not hard to read and has lots of picture examples.
"Colorectal liver metastases: radiopathological correlation" is harder to read but has lots of pictures of different types of scans compared to pictures of actual resected tumors.
My impression is that on an MRI an expert can have some clues about whether a small cyst is a met or benign, but the CT can only check for the presence and maybe the size of the thing. Another option is ultrasound. Much easier to get.
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